The present invention relates to an X-ray apparatus for medical use, and more particularly to a real-time digital radiographic apparatus (hereinafter referred to as real-time DR apparatus) in which a television (TV) camera device is used as an image input device to pick up an X-ray image in real time and the X-ray image is processed to make a diagnosis.
In many regions of the field of recent X-ray diagnosis apparatuses for medical use are utilized with a DR apparatus in which an X-ray image is subjected to a digital image processing after conversion thereof into an electrical signal and subsequent A/D conversion of the electrical signal and is then displayed on a CRT display or printed on a photographic film to make a diagnosis.
Especially, the combination of a TV camera device and an X-ray image intensifier (hereinafter referred to as X-ray II) used for reducing an X-ray dose rate per one image or frame and for acquiring a fluoroscopic image mainly utilized to determine a location to be imaged has been remarked for a long time as an image input device for a DR apparatus since the combination makes it possible to conveniently convert X-ray image information into an electrical signal in real time. In recent years, such a combination has been widely utilized at the scene of labor in medical care as an image input device for a digital fluorographic apparatus (DF apparatus) which is one kind of real-time DR apparatus and in which a subtraction operation between images picked up before and after the injection of a contrast agent into a blood vessel is performed to depict an angiography having an excellent contrast resolution, as has been disclosed by U.S. Pat. No. 4,204,225.
In other words, a DR apparatus needs both the above-mentioned fluoroscopic image and a radiographic image which is an X-ray image of better image quality obtained with the X-ray dose rate per one frame enhanced to about 1000 times as high as that upon fluoroscopic monitoring and which a doctor observes to make a diagnosis.
U.S. application Ser. No. 220,978 filed on July 18, 1988 by applicants which are partially overlapped by the applicants of the present application, has proposed an X-ray TV device capable of selecting one of a plurality of imaging modes between which each of the spatial resolution or the number of scanning lines per one frame and the frame rate is different.
On the other hand, the present application has a relevancy to U.S. application Ser. No. 356,419 filed on May 25, 1989 by applicants a part of which are the same as the applicants of the present application and assigned to the assignee of the present application. This U.S. Application has proposed an X-ray TV device in which an image pickup tube is used within a range of target voltages which cause avalanche multiplification useful for improving the sensitivity of a TV camera and an X-ray TV device in which a target voltage upon fluoroscopic monitoring and a target voltage upon radiographic imaging differ from each other so that avalanche multiplification is produced only upon fluoroscopic monitoring and is not produced upon radiographic imaging.
Also, JP-A-60-180284 laid open on 1985 has proposed an X-ray TV camera device in which a target voltage of an image pickup tube is changed in accordance with an X-ray dose rate.